The invention relates to inputting symbols from a keyboard or a keypad and is particularly, but not exclusively, related to inputting symbols which are not part of the Latin alphabet. In one embodiment the invention is used in the input of characters from character-based languages, such as Chinese hanzi characters and Japanese kanji characters.
Using a keyboard to input characters (also referred to as ideograms) from character-based languages such as Chinese has presented difficulties for some time. There are more than 20 000 Chinese characters and of them about 5 000 to 12 000 are currently commonly used. Therefore, it is not practical to provide a keyboard having a one-to-one correspondence between individual keys and individual characters.
In current methods of inputting Chinese characters into electronic devices having a keyboard (for example a computer), it is known to employ indirect input by describing characteristics of a Chinese character and then selecting a particular Chinese character prompted in a candidate list which is presented to a user. This prompting is performed by software specially written for input of ideogram characters which is referred to as a Front End Processor (FEP) or an Input Method Editor (IME). An FEP interprets an input string from the user and prompts to the user a candidate list of the Chinese character(s) which match the input string or description. The user can then select the correct candidate (if it is shown) from the list and it is entered into a display as the selected character. The candidate can be more than one character. It may be a phrase.
Different ways of describing characters provide the bases of different Chinese input methods. Characters are either described phonetically in which Chinese characters are inputted by describing the associated pronunciation or they are described in terms of character shape in which Chinese characters are inputted by describing the graphical construction or shape of the character. In the People""s Republic of China, the method used to describe pronunciation is Pinyin, which literally means xe2x80x9cspelling the pronunciationxe2x80x9d. This is a phonetic representation of Chinese characters by a Latin alphabet in conjunction with accent marks. Another phonetic description approach is Zhuyin (Bopomofo). This is a phonetic representation of Chinese characters by 37 specific Bopomofo symbols and tone marks.
Because most of the existing Chinese input methods were originally designed for PC keyboards, the number of the basic input symbols or input codes normally matches the number of keys present on a standard QWERTY format keyboard. The table below gives the number of keys required for some of the more popular Chinese input methods.
If a character input method requires more basic input symbols than there are number of keys on a keypad, the first step of inputting the description will encounter a bottleneck. This is caused by more than one symbol being associated with one key which results in repeat or multiple keystrokes being required to input particular symbols.
The problems presented by keyboard input of characters are particularly acute in relation to inputting characters into mobile communication terminals such as mobile phones. This is because of the restricted number of keys (often less than twenty) present in the keypads of such terminals. Since the number of symbols required is often greater than twenty, this can cause the bottleneck described above. Furthermore, since the displays of such terminal are usually small, this can present further difficulties, especially if there needs to be interaction between the terminal and a user of the terminal during the input of symbols and characters.
In the table above, the simple five stroke method is referred to. A stroke is the smallest graphic element to construct a Chinese character and is a complete stroke by a writing tool without lifting it from a writing surface. There are five basic strokes. In the case of a mobile phone, the simple five stroke input method is the one whose input codes can be easily mapped to a phone keypad. However, it is the slowest method to use.
Pinyin is a popular method for inputting Chinese characters into electronic devices because it uses symbols from the Latin alphabet to describe the characters and there are only 413 pronunciations (without using tone marks) for the 6763 commonly used characters in the national standard of the People""s Republic of China, GB2312-80. This means Pinyin has only 413 words in its vocabulary which need to be described.
An example of Pinyin will now be given. If a user wants to input the characters meaning xe2x80x9cmiddlexe2x80x9d or xe2x80x9ccentrexe2x80x9d, he uses letters or symbols from the Latin alphabet to enter the Pinyin pronunciation xe2x80x9czhongxe2x80x9d. The FEP receives this input string and identifies a number of characters which have this pronounciation. These characters or candidates are presented to the user in the from of a candidate list. The Latin letters input by the user and the candidate list are shown in FIG. 1 which represents part of a user interface. This represents a typical situation in which there is more than one candidate available for a given input string. The average number of candidates matching a given input string of an input method is called the Input Coding Redundancy Rate (ICRR). The higher the ICRR, the longer the candidate list a user will receive for an input string, and so the greater number of candidates the user has to scroll through in order to find the correct character. High ICRRs slow down the speed at which characters can be input.
Phone keypads generally have a key layout corresponding to that shown in FIG. 2. A set of symbols (or an alphabet) is assigned (or mapped) to most or all of the keys. For any particular key its alphabet of assigned symbols forms a queue or loop. Within a predefined time-out period, a user presses the key an appropriate number of times sequentially to select a desired symbol in the alphabet. The symbol is then indicated in a display. The symbol is entered into the display if the time-out period expires or if a different key is pressed.
It is time-consuming to input strings of symbols into mobile phones and so methods have been developed to reduce the number of keystrokes that are required. In a method commonly known as T9 provided by Tegic Communications, Inc., input occurs as xe2x80x9cone alphabet one key strokexe2x80x9d. A user identifies the key on which a desired symbol is present and presses that key once. A particular alphabet of three or four symbols is typically associated with that key. This method has been adapted to use the Pinyin system to input Chinese characters. An example will now be given. If a user wants to input the Pinyin string xe2x80x9cgaoxe2x80x9d, he needs to press the keys 4, 2, 6 on the keypad. The method identifies the Pinyin strings which are permissible and can be formed by the alphabets from keystrokes 4, 2, 6 and displays all of them to the user. In this example the permissible Pinyin strings are xe2x80x9cganxe2x80x9d, xe2x80x9cgaoxe2x80x9d, xe2x80x9chanxe2x80x9d, and xe2x80x9chaoxe2x80x9d. All characters which match the permissible Pinyin strings are then indicated as candidates.
A disadvantage of T9 is that a long candidate list is often generated for a given input. This problem becomes worse as the input string becomes shorter. For Chinese input, T9 presents a list of all Chinese characters as candidates if they match any of the possible combinations for the keys which have been pressed. For example, if keys 7 and 4 are pressed, all characters with Pinyin of xe2x80x9cpixe2x80x9d, xe2x80x9cqixe2x80x9d, xe2x80x9crixe2x80x9d, xe2x80x9csixe2x80x9d are indicated, which makes a very long candidate list.
T9 has other disadvantages. It does not give clear feedback in response to user input. This is usually desirable in Chinese input because it is an interactive process in which the user should be able to correct input according to the displayed candidate list. Although T9 tackles the problem of duplicate keystrokes for Pinyin input, it does this at the cost of a long candidate list, and thus a higher ICRR. This means that a user often has to scroll through a long candidate list to find a desired Chinese character. This disadvantage is a particular problem with mobile phones because a small display limits the number of candidates which can be displayed at one time.
T9 has also been applied to Bopomofo input in which the 37 Bopomofo symbols are assigned or mapped to the keys of phone keypad. Besides having similar problems to those discussed above in relation to Pinyin, there is a further problem in that the Bopomofo keypad mapping is totally random from the point of view of a user. The user has no easy way of knowing where each Bopomofo symbol is located, especially if they are not all printed on the keypad due to restrictions in space.
Another method used in the input of Chinese characters uses context sensitive input that predicts the next Chinese character according to the context and a Chinese word database. In this approach, analysis is carried out at the level of the Chinese (ideogram) characters and not at the level of input symbols. This approach can be illustrated by the following example. The example is given in English simply for the purposes of explanation.
A user wants to input the text xe2x80x9cread bookxe2x80x9d. After the user has inputted the word xe2x80x9creadxe2x80x9d, the software prompts words which are likely to follow xe2x80x9creadxe2x80x9d, for example xe2x80x9cbookxe2x80x9d or xe2x80x9cnewspaperxe2x80x9d. If the correct word is indicated, it may be chosen by a user.
A method of inputting symbols and characters is disclosed in GB 2 333 386. A terminal is provided with a probability table which gives a list of the most probable Latin symbols which follow each of the 26 Latin symbols and the xe2x80x9cspacexe2x80x9d symbol. During input of text, on inputting a Latin symbol, a user is presented with a list of all of the Latin symbols in an order determined by the probability of being the next symbol rather than being in a default, for example alphabetical, order. A problem with this method is that the user is presented with a long list of symbols from which to choose a particular symbol.
It is clearly desirable to provide an effective method for inputting characters. Such a method should be easy to learn and to use, it should have a low ICRR and it should have a short average input code length per character. Unfortunately, the above requirements often conflict with each other and it is difficult to provide a character input method which is optimised for all factors.
According to a first aspect of the invention there is provided a method of inputting characters into a terminal the terminal having a plurality of keys at least one of the keys representing a plurality of different symbols in which use of a key to make a previous selection of a symbol is used to determine those symbols represented by a key which are selectable in a subsequent selection.
The term xe2x80x9csymbolxe2x80x9d includes any graphic glyph which can be inputted directly from a keyboard or a keypad. Symbols include alphabets, digits, and basic character input elements such as Bopomofo symbols, character strokes and tone marks. Symbols can be inputted directly from a keyboard and do not require an FEP. Characters, for example hanzi and kanji, need to be input via an FEP.
Preferably a number of the keys have associated with them an alphabet of different symbols which can be accessed and indicated in a display by means of single or multiple key selections or key presses of the keys. The previous selection may result in the alphabet or alphabets of symbols for one or more of the keys being limited.
The key used in the previous selection may be the same key as the key used for the subsequent selection. Alternatively, the keys may be different. The symbols in the previous and subsequent selections may be the same or may be different.
Preferably the method is used to input ideogram characters. It may be used to input Chinese characters (hanzi). Alternatively it may be used to input other characters such as those used in Japan (kanji), Korea or elsewhere. The method is not restricted only to the input of characters and may be used to input letters to form words in the Latin alphabet. According to a second aspect of the invention there is provided a user interface for inputting characters into a terminal the terminal having a plurality of keys at least one of the keys representing a plurality of different symbols in which a symbol is selectable by using a key to make a first selection and a processor is used to determine those symbols represented by a key which are selectable in a second subsequent selection.
According to a third aspect of the invention there is provided a terminal for receiving input of characters the terminal comprising a processor and a plurality of keys at least one of the keys representing a plurality of different symbols in which a symbol is selectable by using a key to make a first selection and the processor is used to determine those symbols represented by a key which are selectable in a second subsequent selection.
Preferably the terminal is a mobile terminal. It may be a mobile phone, a smart phone, a personal digital assistant, a laptop, an electronic notepad, a pager or some other terminal which accepts input from a plurality of keys. In an embodiment in which it is a mobile phone, it may be a cellular mobile phone for connection to a cellular telephone network.
The invention is particularly suitable for terminals which have a small keypad. In this context small means that some of the keys of the keypad have associated with them more than one symbol. This may be less than twenty keys and in certain embodiments may be about twelve keys which are used for, and may be dedicated to, the input of symbols.
In the invention, all the elements which have already been inputted by the user are assumed to be correct and fixed unless the user chooses deliberately to amend them. It only predicts the next symbol which can appear. It is forward-prediction and does not change input which has already been inputted.
Compared to the T9 method, the invention may slightly increase the number of keystrokes required for inputting symbols. However, to compensate, the invention provides a smaller IRCC than T9 and so the number of keystrokes required in total to find a particular Chinese character is reduced. The candidate list may be reduced by an amount in the region of 50%. This provides a significant advantage to devices having a small display because it is rather difficult and slow to scroll through the candidate list in such device. If a single scroll step up or down is considered to be a keystroke, this invention may require fewer keystrokes than the T9 method. In addition, the invention provides positive feedback to the user to guide the input or provide an indication of errors.